1. Field of the Invention
The present invention relates to a method of sealing lamps such as tipless halogen lamps or tipless metal halide lamps without using a tip tube.
2. Description of the Prior Art
FIG. 26 shows a conventional halogen lamp (B') having a typical configuration wherein sealing foils (10') are respectively embedded in seal portions (13') of a lamp envelop (1'), and one end of each sealing foil (10') is welded to a lead portion (21') of a filament (6'), while the other end thereof is welded to a corresponding outer lead pin (11') extending to project outwardly from the seal portion (13').
It has been a conventional practice to seal this type halogen lamps in the following manner. As shown in FIG. 25, an upper open end of a lamp envelop (1') is closed by a lid (30') and an outer lead pin (11') is fixed using a clip (31'). Then, an non-oxidizing gas such as nitrogen, argon, or a mixture of such gas with hydrogen is supplied through a gas supply tube (20') connected to a tip tube (29') into the lamp envelop (1') and discharged from a lower end of the lamp envelop (1') to keep the inside of the lamp envelop (1') in a non-oxidizing atmosphere. In this state, the lower end portion of the lamp envelop (1') is heated so as to be softened, and the end thus softened is pinch-sealed. Subsequently, the lamp envelop (1') is turned upside down, and the same operations as above are repeated, thereby sealing opposite ends of the lamp envelop (1'). Then, the gas within the lamp envelop (1') is sucked out through the tip tube (29') connected to the lamp envelop (1') to provide a high vacuum in the lamp envelop (1'). After necessary operations such as washing by a non-oxidizing gas are completed, the lamp envelop (1') is filled with a required gas, and finally the tip tube (29') is cut-sealed at the base portion thereof by heating.
However, such use of tip tube (29') results in a cut-sealed trace (30') of the tip tube (29') formed on a side surface of the lamp envelop, which not only renders the appearance of the lamp poor but also causes an internal strain to be left in peripheral portions thereof, thereby decreasing the pressure resistance of the lamp envelop (1'). Repeating on/off operations of the lamp i.e., repeating heating and cooling of the lamp may eventually cause the lamp envelop to be broken from the cut-sealed trace (30').
Recently, halogen lamps adaptable for commercial voltages of less power consumption have been demanded in many countries. In response thereto, the volume of a lamp envelop can not help being decreased. However, if a tip tube is used in such a lamp envelop of a decreased volume, the lamp envelop can not be sufficiently cooled when it is immersed in liquid nitrogen for cutting the tip tube after a required gas is filled therein, because liquid nitrogen vaporizes due to the heat of a tip-off burner. As a result, the amount of the filling gas becomes insufficient and, hence, sufficient pressurizing of the lamp envelop can not be achieved. Thus, in spite of the recent tendency to increase the pressure of the gas to be filled in the lamp envelop so as to enhance the performance of the lamp such as a brightness and lifetime, the use of a tip tube makes it impossible to increase the filling gas pressure for such a small volume lamp envelop because of the reasons stated above. Further, the presence of the cut-sealed trace of the tip tube causes an internal strain to be left adjacent the trace and, hence, the lamp envelop can not endure such a high filling gas pressure.
Consequently, it has been difficult to significantly enhance the performance of a small-sized halogen lamp of the type using a tip tube.
There exists another problem that the cut-sealed trace of the tip tube causes the scattering of light passing through the trace and the peripheral portion thereof, which leads to a decreased light-converging ability. Such a lamp is not suitable for use as a light source of high-precision apparatus such as a microscope or a measuring instrument. This is also true for the case of a metal halide lamp.
It is, therefore, an object of the present invention to provide a novel method of sealing a lamp such as a halogen lamp or a metal halide lamp, with which: a conventionally required tip tube can be dispensed with thereby providing a lamp envelop free of a cut-sealed trace; and the filling gas pressure can be increased.